Present day engine components must be manufactured more simply at significantly reduced costs while achieving superior results in order for engine manufacturers to remain competitive. Unfortunately, exhaust manifolds and port liners that have become less complicated have either failed to produce superior heat insulation capabilities or have become less durable, increasing associated replacement costs.
The heat-insulated port liner for a device composed of a cast metal disclosed in U.S. Pat. No. 4,676,064 by Yoshinori Narita et. al. on Jun. 30, 1987 includes a tubular port liner composed of a ceramic material, a first covering layer disposed on the outer surface of the liner and composed of refractory fibers, and a second covering layer disposed on the outer surface of the first covering layer and composed of a metal having a melting point not lower than the melting point of the cast metal. The port liner is made from a material having a low coefficient of thermal expansion and high thermal resistance, such as, aluminum titanate. Unfortunately, no range is given for the coefficient of thermal expansion needed for the port liner used with a cast aluminum cylinder head. It is well known that the melting point of aluminum is lower than that of cast iron and that aluminum titanate can be effectively used with molten aluminum. However, aluminum titanate may only be successfully cast in very simple geometries due to the additional stresses it will encounter upon exposure to molten cast iron. Further, the stability of aluminum titanate varies with the composition. The port liner disclosed by Narita could be destroyed during the casting process if used with a cast iron cylinder head, depending upon the complexity of the geometry and the composition of the aluminum titanate.
Additionally, since the first covering layer is unsupported, settling of the refractory fibers occurs when the fibers are exposed to typical engine vibration experienced during operation. This settling effect limits the effectiveness of the insulation and may lead to the destruction of the entire insulation layer. Once destroyed, the insulation would be free to disintegrate and enter the exhaust passage.
A method and apparatus for insulating the exhaust passage of an internal combustion engine is disclosed in U.S. Pat. No. 4,206,598 by Vemulapalli D. Rao on Jun. 10, 1980. A three-zone liner assembly is provided with an outer zone comprised of a room temperature vulcanizing silicone sleeve, an inner zone comprised of a stamped and seam welded high strength Al--Cr-steel alloy, and an intermediate zone consisting of a ceramic wool mat. The Al--Cr-steel alloy utilized has high thermal expansion, which would cause problems in use as an exhaust manifold or port liner, due to the high temperature applications and the thermal growth differences relative to the cylinder head. The Al--Cr-steel alloy material could fatigue and crack at those temperature ranges unless exhaust bellows or slip joints are used in conjunction with the Al--Cr-steel alloy material. The exhaust bellows and slip joints are undesirable due to cost and gas leakage. Also, the intermediate zone consisting of the ceramic wool mat of insulation is encased within the seam welded inner zone of metal protecting the insulation from damage. However, if the weld fails, the insulation is subjected to possible damage which, as with Narita, would cause disintegration of the insulation and destruction of the entire insulation layer.
Further, with the above insulation element, the insulation is applied externally to the exhaust manifold or port liner. This creates service difficulty when the insulation needs to be replaced every 3000 to 5000 hours.
An improved apparatus for insulating the exhaust passage of an internal combustion engine is disclosed in U.S. Pat. No. 5,404,716 by Alan W. Wells et al. on Apr. 11, 1995. The insulating element is quilted and has ceramic fiber encased within fiberglass. This insulating element is then extended about the liner of a manifold. The liner in this invention may be ceramic or stainless steel, preferably stainless steel. A housing can then be cast or assembled around the liner and insulating element. An apparatus and method for insulating port liners was disclosed in U.S. Pat. No. 5,552,196 by Micheal H. Haselkorn et al. on Sep. 3, 1996. A ceramic port liner is surrounded by an insulating blanket, as described in U.S. Pat. No. 5,404,716. The ceramic port liner and surrounding blanket can then be cast within a cylinder head. During the casting process, the ceramic port liner remains in a softened state.
Neither the Wells et al. and Haselkorn et al. patents address the important issue of supporting the cast-in-place liner made of ceramic material. Casting the housing around the ceramic material requires special venting that is not disclosed in either patent.
In addition, there are other problems associated with casting the ceramic liner, wrapped in insulation, into cast iron. These include: sealing, venting, and support.
During casting, the cast iron must not contact the ceramic liner. The molten iron will thermally shock the ceramic material and cause failure. If the ceramic survives the thermal shock, then the solidification and shrinkage(thermal contraction) during cooling will compress the ceramic and cause either the ceramic or cast iron to fail.
Venting is also a problem. The insulation contains a large volume of air that expands when heated by the molten iron. The expanding air will cause large porosity defects in the cast iron if the air is not vented properly. The ceramic liner is impervious to air and prevents the normal venting of the insulation through the sand cores. Therefore, alternative venting routes have to be supplied.
Finally, the ceramic liner needs to be supported after casting. The ceramic liner must be permanently located within the cast iron housing. If the ceramic liner is cast-in without the iron contacting it, the ceramic is essentially floating free, held in place only by the compression of the insulation by the cast iron. The insulation compression may provide some support, by not sufficient support for long-term operation/resistance to engine vibration.
The present invention is directed to overcoming the problems as set forth above.